Generally, an elevator may be driven by an induction motor, and an inverter may be used in the control apparatus to power the motor. While the inverter circuit and its control cannot be ignored for smooth control of the elevator, at the same time, control of the brake is extremely important.
FIG. 6 is a circuit diagram to illustrate an example of the brake control circuit of the prior technology. In FIG. 6, an induction motor 61 is controlled by an inverter circuit 62. Brake 63 has a brake coil 64 which is disposed on the shaft of the induction motor 61. In this diagram, TF is a three-phase transformer for generating the voltage for descending; CON1 and CON2 are labels for rectifying circuits 64a, 64b for forward conversion; C1 and C2 are smoothing capacitors; INV is a label for an inverter 64c for reversing; M1, M1', and M2 are labels for contacts 64d, 64e, 64f of a DC electromagnetic contactor (not shown) which causes the contacts to close in response to a lift brake command; R1 and R2 are labels for resistors 64g, 64h, DIS is a diode 64j; IB is a brake current on a line 64k; and BL is a contact 64m which is turned ON (close circuited) when the brake is completely open. With the brake control member, the voltage of the three-phase input power source to the inverter circuit 62 is lowered by the transformer TF to form a specific AC power source, and the current is converted by the rectifying circuit CON2 to form a braking power source. The rectified power source current, after being restricted by the resistor R1, flows to the brake coil 64 as the brake current IB.
FIG. 7 is a time chart having a common time base to illustrate an example of the operating sequence of each part of the above-mentioned brake control circuit. In FIG. 7, all commands are ON command at "High". With the brake OPEN command XLB as shown by a waveform 66 in FIG. 7 (a), the contacts M1, M1', and M2 of the electromagnetic contactor become ON (shorted) as shown by a waveform 68 in FIG. 7 (b) for M1 and M1' and a waveform 70 in FIG. 7 (c) for M2. Thus, brake current IB flows as shown by a waveform 72 in FIG. 7(d). As the brake OPEN procedure ends, the contact 64m (BL) is closed as indicated by a waveform 74 in FIG. 7 (e). In response to the BL signal, the contact M2 of the electromagnetic contactor becomes OFF (open circuited), and as a result, the brake current IB will be restricted by the resistor R1.
The time chart of the above-mentioned FIG. 7 is illustrated in more detail in FIG. 8. In FIG. 8, as an elevator operating command MU (Make Up) or MD (Make Down) is issued by an upper level controller (not shown) for elevator up or down travel as indicated by a waveform 76, the gate control of the inverter circuit which drives the induction motor will be started (I1) as shown in FIG. 8 (k) by a waveform 78 after taking into account the chattering of an associated contact of the relay, such as for example about 50 msec later; meantime a DC current to generate a static torque in the motor flows (DRIVE) as indicated in FIG. 8(b) by a waveform 80. At this point, a short time interval is set until a brake OPEN command signal (XLB) is initiated, as shown by a waveform 82 in FIG. 8 (c), to start lifting the brake and to initiate detection of the secondary time constant of the motor. The time of initiation is 50+670 (msec) after MU or MD went ON for the example illustrated in the driving.
As brake OPEN command (XLB) is generated by the motor control device, the electromagnetic contactor is triggered, as explained already in FIG. 6, and this will turn ON (close or short circuit) the contacts M1, M1' and M2. Thus, brake current IB flows to the brake coil 64 as indicated by a waveform 83 in FIG. 8(j) and the brake will be released. This will permit the elevator car to move.
The BL contact 64 is the contact which will become ON (closed) when the brake operates mechanically as indicated by a waveform 84 in FIG. 8(d). Since there is some time lapse from the contacting part of the actual brake, the brake lifted (BL) signal will be in the "brake lifted" status at the timing which is corrected for lift brake (LB) time or drop brake (DB) time, as illustrated by a waveform 86 in FIG. 8(e), and thereafter the elevator control apparatus will control the speed or the position. In FIG. 8(f), a DV waveform 88 is a velocity command signal. FIG. 8(g) illustrates the brake torque by a TB waveform 90. FIG. 8(h) shows a speed feedback signal waveform 92 and FIG. 8(i) shows a dictated torque current waveform 94.
As the elevator reaches a target floor, a command is issued to turn OFF the brake OPEN signal (XLB) after a certain period, for example, after 500 msec. Thus, the contacting points M1 and M1' of the electromagnetic contactor are set at the OFF (open circuit) position, and this will cut off the current IB to the brake coil 64. The brake is closed, and the elevator control apparatus will close the brake circuit at the timing (BL+DB time), turn off the gate control of the main circuit, and enter into a status of waiting for receipt of a succeeding operational command.